Heater unit for cathode

ABSTRACT

Presented is a heater unit adapted for use in conjunction with a cathode.

United States Patent 1191 Barraco et al.

[ Oct. 21, 1975 HEATER UNIT FOR CATHODE [76] Inventors: Anthony J. Barraco, 5499 Blossom Tree Lane, San Jose, Calif. 95124; Martin E. Wolfe, 2121 Stratford Way, San Mateo, Calif. 94403 22 Filed: Apr. 5, 1974 21 Appl. No.: 458,1 12

[52] U.S. Cl. 313/271; 313/273; 313/341 [51] Int. Cl. H01J 1/88; H01J 19/42 [58] Field of Search 313/271, 273, 337, 338,

[56] References Cited UNITED STATES PATENTS 3,748,522 7/1973 Geppert 313/338 FOREIGN PATENTS OR APPLICATIONS 877,756 9/1961 United Kingdom 313/338 Primary Examinei' saxfield Chatmon, Jr. Attorney, Agent, or Firm-John J. Leavitt [5 7 ABSTRACT Presented is a heater unit adapted for use in conjunction with a 'cathode.

13 Claims, 4 Drawing Figures HEATER UNIT FOR CATl-IODE BACKGROUND OF THE INVENTION Through the years, and as technology has become more and more sophisticated, many attempts have been made to produce a micro-miniature cathode to satisfy the requirements imposed by miniaturization of sophisticated electronics. So far as is known, the art has not progressed to the point of fabricating heater units or filaments through use of photoetching techniques. Accordingly, one of the objects of the present invention is to provide as an article of manufacture a heater unit or filament manufactured through the photoetchmg process.

In the miniaturization of electronic components, it is frequently necessary that micro-miniature cathodes be utilized. Such cathodes require that they be heated to a temperature conclusive to electron emissivity, and the miniaturization of such cathodes has heretofore been limited by the inability to produce a heater unit or filament of correspondingly small size, and which will provide the heat energy required to raise the cathode to emissivity. Accordingly, another object of the present invention is to provide a heater unit for microminiature cathodes.

One of the critical factors that has caused the cost of sophisticated electronics to remain relatively high has been the difficulty of fabricating electronic components. Frequently, such components must be individually manufactured in whole or in part, thus contributing to the labor cost involved. One detrimental aspect of high labor content and attendant high labor cost has been the exodus from the United States to foreign countries of the assembly function for electronic and other components by labor that costs significantly less than the labor in the United States. Accordingly, another object of the'present invention is to provide a heater unit which may be fabricated in large quantities by assembly line mass production techniques utilizing a minimum of labor in such production while preserving uniform technical parameters.

Heretofore, as far as is known, heater units or filaments have been specifically designed for a given environment. Thus, it has been important to know the power drain caused by a heater unit or filament because the amount thereof is important in the applicability of the overall package. So far as is known, a heater filament has not heretofore been available constructed in such a configuration that it may be scaled up or down to satisfy different power levels while retaining substantially the same configuration. Accordingly, another object of the invention is to provide a filament for heating a planar cathode which may be fabricated in micro-minature size having an overall diameter of approximately 0.040 inch or sealed to have an overall di ameter of 2, 3 or 4 inches while retaining the same configuration.

Still another object of the invention is the provision of a method by which a flat heater filament suitable for use with micro-miniature cathodes may be mass produced so that each heater filament has essentially the same characteristics.

In the realm of micro-miniature electronics, one of the problems that has been difficult of solution and which has contributed to the high cost of labor in assembly of such micro-miniature electronic components has been tediousness of the assembly, made so because of the exceedingly small size of the component. Accordingly, a still further object of the present invention is to provide a method and means by which assembly of a micro-miniature heater filament into a finished component is facilitated so as to minimize tedious hand work.

Because of limitations in conventional manufacturing techniques for conventional cathode heaters, only a very limited number of materials have heretofore been useful for cathode heaters. Accordingly, it is another object of the invention to provide a method of manufacture for cathode heaters which will permit utilization of any metal having a melting point about 1600C. as a cathode heater.

BRIEF SUMMARY OF THE INVENTION In terms of broad inclusion, the heater unit or filament of the invention comprises a continuous elongated member fabricated from an appropriate electrically resistive refractory material such as tungsten or tungsten/rhenium alloy, having a flat configuration formed by a multiplicity of interconnected sections arranged in serpentine fashion. In one aspect of the invention the elongated electrically resistive material constitutes a generally rectangular ribbon of tungsten/- rhenium alloy. In another aspect of the invention, the heater filament comprises a serpentine pattern of refractory ribbon material formed through the process of photo-etching. In still a third aspect of the invention, the invention contemplates the method of fabrication of a flat ribbon-like heater filament from a flat sheet of refractory material such as tungsten or tungsten/- rhenium alloys, or other materials equivalent thereto and having a melting point about 1600C., such as tantalum, iridium or molybdenum, the manufacturing process proceeding through photoetching to produce a continuous filament having adjacent sections arranged in planar alignment in serpentine fashion, together with the supporting and electrical leads therefor and a mounting portion attached thereto to facilitate assembly of the heater filament when fabricated in microminiature size. In another aspect of the invention the heater filament is fabricated through a photoetching process from refractory sheet material so as to provide chamfered edges on the generally rectangular ribbon filament portions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged plan view of the heater unit or filament, portions of the support legs being broken away to reduce the size of the view.

FIG. 2 is a plan view showing the heater unit or filament in its entirety mounted on a mounting plate which facilitates handling of the component.

FIG. 3 is a cross-sectional view through one section of the filament taken in the plane indicated by the line 3-3 in FIG. 1.

FIG. 4 is a cross-sectional view similar to FIG. 3, but showing the section formed with chamfered edges.

DESCRIPTION OF THE PREFERRED EMBODIMENT In terms of greater detail, the heater unit or filiment of the invention is designated generally by the numeral 2, and includes a centrally disposed heater section 3 constituting a single continuous ribbon 4 fabricated from an electrically resistive material such as one of the refractory metals, including tungsten, tungsten/- rhenium, alloys thereof, or equivalent refractory materials which may be heated to incandescence by the passage of an electric current therethrough and which have a melting point above 1600C. Examples of such other suitable materials include tantalum, iridium and molybdenum. As viewed in FIG. 2, the central heater portion 3 is electrically and mechanically connected by radially extending legs 6, 7 and 8, the inner end portion 9 of the leg 6 integrally connecting the terminal portion 12 of the ribbon 4 at a point spaced from its extreme end so that an anchor portion 13 remains between the extreme end of the ribbon and theassociated end portion 9 of the supporting and electrically connected leg 6.

From this point, it will be seen that the ribbon filament is arranged to provide continuous and electrically serially connected sections arranged in serpentine fashion so that the sections of ribbon filament lie distributed over a predetermined area defining the external limits of the heater unit. At its end opposite the terminal portion 12, the ribbon filament is provided with a terminal portion 14 integrally connected to the end portion 16 of the heater leg 7, there again being provided a short anchor stub 17 next adjacent the end portion 16 of the heater leg similar to the lug 13. It will thus be seen that by passing an electrial current through the support and electrical lead legs 6 and 7, the entire ribbon may be raised to incandescence. In this respect, it should be noted thast each of the legs 6, 7 and 8 are fabricated from the same refractory material as the central heater portion 3 of the filament and are proportioned to provide mechanical support for the centrally disposed heater portion while simultaneously functioning as a heat dam to prevent the loss of heat from the central heater section through conduction along the lead legs.

For additional support, and where desirable to provide an additional electrical connection, the heater leg 8 is provided with a root portion 18 somewhat wider than the main portion of the leg, the root portion being integral with the ribbon filament 4 at about its midpoint. It will thus be seen that the heater portion 3 of the heater filament may be provided with three supports to minimize the tendency of the heater filament to be physically displaced from associated structure when mounted in its final environment. It should be understood however that two legs 6 and 7 are electrically and mechanically adequate, and that the third leg 8 may be dispensed with entirely, or be electrically disassociated from the heater unit.

To facilitate connection of the heater filament thus formed into a supporting structure and into an electrical circuit, each of the legs 6, 7 and 8 is provided with a generally circular pad 19 integral with each associated leg, and integral through a narrow neck portion 21 with a larger circumscribing plate portion 22 formed from the same material from which the heater filament is fabricated. As illustrated in FIG. 2, the plate portion 22 is conveniently circular in its configuration, having an outer periphery 23, and being provided at approximately 120 interval with apertures 24 formed adjacent the outer periphery. Where desired, an additional pair of apertures 26 may be provided as shown. To isolate the heater unit from the plate 22 except through the narrow neck portions 21, the plate is cut away to provide a generally triangular aperture 27 within which the heater unit is centrally disposed.

It will thus be seen that when the heater filament is fabricated in micro-miniature size, say from material having a thickness of only 0.001 inch and an overall diameter of the heater portion 3 of only 0.040 inch, the surrounding plate 22 provides the means by which the exceedingly small micro-miniature heater filament may be individually handled without difficulty.

In the fabrication of the heater filament thus described, the configuration illustrated in FIG. 2 is photographically reproduced and exposed on a sheet of refractory material treated with a photo sensitive compound. After exposure, the photo sensitive sheet of refractory material is treated to harden the impression or pattern photographically impressed thereon, and thereafter the sheet of refractory material is subjected to an etching process which removes all of the refractory material with the exception of the pattern photographically reproduced thereon and which is illustrated in FIg. 2. It will of course be understood that depending on the size of the heater filament being fabricated, a multiplicity of such components in the pattern indicated in FIG. 2 may be distributed over a relatively large sheet. For instance, assuming the outer periphery 23 of the unit illustrated in FIG. 2 to have a dimension of 0.372 inch, approximately 780 such units can be produced from a single 8% X 13 inch sheet of refractory material. More importantly, such sheets incorporating such a large number of units, may be handled as a single unit, thus obviating the necessity of handling each individual heater filament per se.

Having thus described the invention, what is claimed to be novel and sought to be protected by letters patent is as follows:

1. An electrically energizable cathode heater unit comprising:

a. an elongated electrically resistive filament formed from a sheet of suitable material to provide a plurality of serially connected turns arranged in serpentine fashion; and

b. a pair of support legs formed from the same sheet of suitable material as the filament and integral with selected portions of said filament and adapted to function also as electrically conductive terminal leads for said heater unit.

2. The combination according to claim 1, in which said serially connected turns all lie in a common plane.

3. the combination according to claim 1, in which a third support leg is provided integral with said filament intermediate said first mentioned pair of support legs.

4. The combination according to claim 1, in which said filament is fabricated from a material selected from the group consisting of tungsten, molybdenum, tantalum, iridium, rhenium, and alloys thereof.

5.. The combination according to claim 1, in which each of said legs is integral at one end with a selected portion of said filament and extends radially outwardly therefrom in the same plane, and integral pad means are provided on the outer end of each of said support legs, each said pad having a transverse dimension in relation to said leg substantially greater than the trans verse dimension of the leg.

6. The cimbination according to claim 1, in which three such support legs are provided connected to said filament at selected intervals therealong and extending radially away therefrom in the same plane, and a mounting plate circumscribing said heater unit and integrally connected to the end of each of said support legs at its end remote from said heater unit and lying in the same plane as said support legs.

7. The combination according to claim 1, in which said filament is a ribbon generally rectangular in configuration, having a thickness of approximately 0.001 inch and a width of approximately 0.0015 inch, the spacing between turns of said filament being in the order of 0.002 inch.

8. The combination according to claim 1, in which said material constitutes an alloy of tungsten and rhenium, the quantity of rhenium to tungsten being in the range of 3% to 25% by weight.

9. The combination according to claim 1, in which said electrically resistive material is formed from a metal having a melting point above 1600C.

10. The combination according to claim 1, in which said electrically resistive material is molybdenum.

11. The combination according to claim 1, in which said pair of support legs are integral with opposite end portions of said filament, and an anchor tab is provided between the extreme end of the filament and the associated end portion of the support leg.

12. The combination according to claim 1, in which said resistive filament after formation is rectangular in cross-section.

13. The combination according to claim 1, in which said resistive filament after formation is generally rectangular in cross-section and is provided with chamfered edges. 

1. An electrically energizable cathode heater unit comprising: a. an elongated electrically resistive filament formed from a sheet of suitable material to provide a plurality of serially connected turns arranged in serpentine fashion; and b. a pair of support legs formed from the same sheet of suitable material as the filament and integral with selected portions of said filament and adapted to function also as electrically conductive terminal leads for said heater unit.
 2. The combination according to claim 1, in which said serially connected turns all lie in a common plane.
 3. the combination according to claim 1, in which a third support leg is provided integral with said filament intermediate said first mentioned pair of support legs.
 4. The combination according to claim 1, in which said filament is fabricated from a material selected from the group consisting of tungsten, molybdenum, tantalum, iridium, rhenium, and alloys thereof.
 5. The combination according to claim 1, in which each of said legs is integral at one end with a selected portion of said filament and extends radially outwardly therefrom in the same plane, and integral pad means are provided on the outer end of each of said support legs, each said pad having a transverse dimension in relation to said leg substantially greater than the transverse dimension of the leg.
 6. The cimbination according to claim 1, in which three such support legs are provided connected to said filament at selected intervals therealong and extending radially away therefrom in the same plane, and a mounting plate circumscribing said heater unit and integrally connected to the end of each of said support legs at its end remote from said heater unit and lying in the same plane as said support legs.
 7. The combination according to claim 1, in which said filament is a ribbon generally rectangular in configuration, having a thickness of approximately 0.001 inch and a width of approximately 0.0015 inch, the spacing between turns of said filament being in the order of 0.002 inch.
 8. The combination according to claim 1, in which said material constitutes an alloy of tungsten and rhenium, the quantity of rhenium to tungsten being in the range of 3% to 25% by weight.
 9. The combination according to claim 1, in which said electrically resistive material is formed from a metal having a melting point above 1600*C.
 10. The combination according to claim 1, in which said electrically resistive material is molybdenum.
 11. The combination according to claim 1, in which said pair of support legs are integral with opposite end portions of said filament, and an anchor tab is provided between the extreme end of the filament and the associated end portion of the support leg.
 12. The combination according to claim 1, in which said resistive filament after formation is rectangular in cross-section.
 13. The combination according to claim 1, in which said resistive filament after formation is generally rectangular in cross-section and is provided with chamfered edges. 